This invention relates to a wide room mirror used by attaching to an existing room mirror arranged in all vehicles including an automobile.
A technique for arranging a room mirror (back mirror) for looking an opposite side in a looking direction without turning a driver's head within each of rooms or compartments of all vehicles including an automobile is conventionally well-known.
A technique for attaching a detachable type mirror having a plane mirror or a curved mirror onto the surface of an existing room mirror is also well-known.
However, as shown in FIG. 29, a region .theta.4 reflected on a conventional existing room mirror 301 is limited to a narrow range just behind a vehicle 303.
When the detachable type mirror having a plain mirror is attached onto the existing room mirror, the reflecting region can be enlarged by increasing a size of the plain mirror. However, the size of the plain mirror is limited since a front viewing field is narrowed when the detachable type mirror is increased in size. Accordingly, it was difficult to greatly increase a region .theta.5 reflected on the plain mirror with respect to the above region .theta.4.
Further, when a convex curved mirror instead of the plain mirror is used as the detachable type mirror, it is possible to enlarge the reflecting region by reducing a radius of curvature of the convex curved mirror. However, the size of a reflected object is reduced by the reduction in the radius of curvature so that it is difficult for a driver to grasp a distance feeling. Accordingly, no radius of curvature of the convex curved mirror can be reduced so much to easily grasp the distance feeling. Therefore, no region reflected on the curved mirror is changed so much in comparison with the region .theta.5 formed when the plain mirror is used.
Thus, when the reflecting region formed by the room mirror or the detachable type mirror is narrow, a slanting backward dead angle region 307 unable to be seen without turning the driver's head is increased in size. Therefore, there is a case in which a vehicle 203 is completely located within the dead angle region 307. In this case, the driver must directly see the slanting backward vehicle 203 by turning the driver's head slantingly backward to confirm existence or nonexistence of the slanting backward vehicle 203. Accordingly, there is a fear of a reduction in safety at a driving time of the vehicle. A side mirror arranged outside the vehicle room is known to compensate the viewing field of the room mirror. However, it is generally impossible to sufficiently compensate the above dead angle region 307 by the side mirror.